MATLAB: Convert byte to double

byte conversion

Hi, I have somae data in a byte format that i want to convert to double format. Does anyone know how to do this in matlab?

I have read the data in to a char, where every 8 characters should represent a double.

My data looks like this :

QAAAAAAAaIBAAAAAAADQgUAAAAAAAHCCQAAAAAAAsINAAAAAAAAohEAAAAAAAKCEQAAAAAAA4IVAAAAAAABgiEAAAAAAAJCKQAAAAAAAMItAAAAAAADQi0AAAAAAAGCNQAAAAAAAUI5A

/Malte

Best Answer

I found out that the string was in base64 code, which i have decoded using the base64decode function from: http://code.google.com/p/fieldtrip/source/browse/trunk/external/gifti/@gifti/private/base64decode.m?r=3261

I could then transform the uint8 array produced by base64decode with the typecast function.

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MATLAB: Convert 4char to one double values

There are multiple methods of doing the conversion, depending on the byte order that the numbers were stored in compared to the byte order your machine is using.

Are you certain that you want 4 characters to represent a double, not a single ? If double then is the data representation custom or is the data stored as a single but you want a double as output? That is, double is 64 bits which is 8 bytes and single is 4 bytes.

If your data is a multiple of 4 bytes and each byte was stored to an individual character (the usual), and your byte orders match, and the 4 bytes are in the format of a single, then:

double(typecast(uint8(Data), 'single'))

(But easier would be to read it from the file as numeric.)

MATLAB: Why does matlab use 8 bytes to memorize a number like 1 for example

By default if you do not tell MATLAB what datatype to use for a number, it uses IEEE 754 Double Precision floating point representation, which is described in more detail at https://en.wikipedia.org/wiki/IEEE_754

When you use char, MATLAB stores the values in UTF-16, which is representation that uses a minimum of two bytes per code point, with a system for indicating that more bytes may be needed. https://en.wikipedia.org/wiki/UTF-16 Code points up to roughly 55295 can be represented in two bytes (and there are another 8192 later ones with direct representation). This includes characters up to 힣 but does not include some alphabets such as Linear B or Phonecian. https://en.wikipedia.org/wiki/Plane_(Unicode)#Supplementary_Multilingual_Plane -- it is enough to hold most living languages.

Character manupulation and storage is a lot easier when you (usually) do not need to worry about the number of bytes needed to represent characters. Single-byte characters would miss out on a lot of commonly used characters -- for example the Greek characters do not start until about code position 913.

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MATLAB: Convert 4char to one double values

MATLAB: Why does matlab use 8 bytes to memorize a number like 1 for example

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